Braconidae

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Introduction

The Braconidae constitute one of the most species-rich families of insects. Although tropical faunas are still relatively poorly understood at the species level, most taxonomists in this group would agree that a rough, probably highly conservative, estimate of 40-50,000 species worldwide is reasonable as an extrapolation from the current described number of roughly 12,000 species. Among extant groups, the sister group of the Braconidae is the Ichneumonidae, an equally enormous group (Sharkey and Wahl, 1992; Quicke et al. 1999).

The family appears to date from early Cretaceous (assuming Eobracon is properly assigned to family - Rasnitsyn, 1983; Whitfield, 2002), diversifying extensively in the mid to late Cretaceous and early Tertiary, when flowering plants and their associated holometabolous herbivores, the main hosts for braconid parasitoids, radiated (Basibuyuk et al., 1999; Quicke et al., 1999; Belshaw et al., 2000; Whitfield, 2002). The species richness of the family is matched by a morphological diversity virtually unrivalled among the Hymenoptera. They range in size from approximately 1 mm in length to 3-4 cm (not counting the ovipositor, which in some species can be several times as long as the body).

Some of the groups are parts of extensive Müllerian mimicry complexes (Quicke, 1986), and exhibit striking color patterns (some of which are recurrent within regions), while others are among the most inconspicuous of Hymenoptera. The braconids display a bewildering array of wing venation patterns and body forms to stymie the beginning student. Female external genitalia (ovipositor mechanisms) vary considerably intraspecifically and are widely used for species discrimination;

Characteristics

The vast majority of braconids are primary parasitoids of other insects, especially upon the larval stages of Coleoptera, Diptera, and Lepidoptera but also including some hemimetabolus insects (aphids, Heteroptera, Embiidina). As parasitoids they almost invariably kill their hosts, although a few only cause their hosts to become sterile and less active. Both external and internal parasitoids are common in the family, and the latter forms often display elaborate physiological adaptations for enhancement of larval survival within host insects, including the co-option of endosymbiotic viruses for compromising host immune defenses (Stoltz and Vinson, 1979; Stoltz, 1986; Whitfield, 1990; Beckage, 1993, Stoltz and Whitfield, 1992; Whitfield, 2002; Whitfield and Asgari, 2003).

Early larval development in braconids has also yielded surprises, such as the discovery of relatively closely related genera that differ in such import aspects as syncitial versus holoblastic cleavage, normally characterizing major animal phyla (Grbic and Strand, 1998; Grbic, 2000)! Parasitism of adult insects (especially of Hemiptera and Coleoptera) is also known, and members of two subfamilies (Mesostoinae and Doryctinae) form galls on plants (Infante et al., 1995; Austin and Dangerfield, 1998). Several excellent general reviews of braconid biology are available (Matthews, 1974; Shaw and Huddleston, 1991; Shaw, 1995; Wharton, 1993a).

The phylogeny used as the backbone here for accessing the subfamilies is adapted and pasted together, with a great deal of conservative poetic license, from these recent studies. It should not be taken all that seriously, as help is on the way in the form of continuing morphological and molecular phylogenetic studies. The reader is encouraged to consult the literature cited above for more in-depth analysis.

Classification

The higher classification of the Braconidae has been a matter of much dispute. Approximately 40 subfamilies are generally recognized, several of them newly discovered within the last 15 years (Mason, 1983; Quicke, 1987; Whitfield and Mason, 1994). Several subfamilies (e.g., Aphidiinae, Alysiinae, Apozyginae) have at one time or another been recognized as separate families. In general there is agreement on the basic subfamily or tribal groupings, with the exception of the "hormiine" and "exothecine" groups of genera (Whitfield, 1992; Quicke, 1993; Wharton, 1993b), but disagreement on the ranking or inclusiveness of some groups, since our understanding of the phylogeny of the family is not yet robust. There is a general perception that the number of recognized subfamilies has become inflated, while the tribal rank has been underutilized. An attempt has been made to address this problem (Wharton, 2001), but requires further phylogenetic testing.

Grbic, M. and Strand, M. R. 1998. Shifts in the life history of parasitic wasps correlate with pronounced alterations in early development. Proceedings of the National Academy of Sciences of the USA 95: 1097-1101.

Mardulyn, P. and J. B. Whitfield. 1999. Phylogenetic signal in the COI, 16S and 28S genes for inferring relationships among genera of Microgastrinae (Hymenoptera: Braconidae): evidence of a high diversification rate in this group of parasitoids. Mol. Phylo. Evol. 12: 282-294.

Shaw, M. R. and T. Huddleston. 1991. Classification and Biology of Braconid Wasps (Hymenoptera: Braconidae). Handbooks for the Identification of British Insects, Vol. 7, Part 11. Royal Entomological Society of London.

Page: Tree of Life
Braconidae.
Authored by
James B. Whitfield, Won-Young Choi, Alejandro A. Valerio, Josephine Rodriguez, and Andrew R. Deans.
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